1. Technical Field
The present invention relates to the design of hard disk drives to minimize power consumption while maintaining performance levels. More particularly, the present invention relates a technique for minimizing power consumption by one or more processors controlling the disk drive.
2. Related Art
A hard disk drive assembly is a mass-storage device from which data may be read and/or written. Typically the hard disk drive includes one or more randomly accessible rotatable storage media, or disks upon which data is encoded. In a magnetic disk drive, the data is encoded as bits of information using magnetic field reversals grouped in tracks on the magnetic hard surface of rotating disks. A transducer head supported by an actuator arm is used to read data from or write data to the disks. A voice control motor (VCM) attached to the actuator controls positioning of the actuator, and thus the transducer head position over a disk.
Data read from the disk or written to the disk is provided through circuitry to a processor. Servo position data read from the disk is processed by the processor, enabling the processor to provide servo current command signals to control the VCM for proper positioning of a transducer head relative to a disk
When a hard drive system is intended to be mobile, and includes an internal battery, the system is typically set to operate at a low power level. With a low power, overall performance is typically sacrificed in return for maximizing battery life. For non-portable hard disk drives not requiring batteries, system power levels are not a significant issue and the system power levels can be set high to maximize performance.
One way to reduce power consumption is to reduce the core clock frequency of a component. Power varies approximately linearly with clock speed and by the square of voltage as evidenced by the following equation:Power=(Total Capacitance×Frequency×Voltage2)/2The operation frequency, and thus power consumption can be linearly adjusted by reducing the clock rate. Adjusting both clock rate and system voltage level can produce approximately cubic reductions in power consumption.
However, it is also desirable to increase the performance level of the system by increasing the processor clock frequency. For a processor of a hard disk drive intended for a battery operated portable device, the processor clock rate is set to facilitate a compromise between reducing power to maintain battery life and maintaining a desired level of system performance.